What is FSH?

What women with PCOS need to know about this hormone

Ovulation
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Follicle stimulating hormone, or FSH, is a hormone released from the pituitary gland in the brain that stimulates an egg follicle to grow each month as part of the menstrual cycle.

Women with PCOS often do not ovulate on a monthly basis due to low FSH levels. If your doctor suspects you may have PCOS, he or she will order blood work for FSH along with other hormone levels prior to diagnosis.

Older women tend to have elevated blood levels of FSH, which indicate ovarian maturing.

This is because greater amounts of the hormone are required for the ovary to recruit and stimulate an egg follicle.

FSH Levels During Your Cycle

Throughout your menstrual cycle, levels of FSH vary. Doctors often test FSH levels at day 3 of your cycle. These are considered your baseline levels.

FSH is part of a complex dance of hormones that includes luteinizing hormone (LH), estradiol, and gonadotropin-releasing hormone (GnRH). FSH stimulates an immature follicle to grow. Once it is grown, it releases estradiol, which signals the release of GnRH and LH, prompting ovulation.

Prior to ovulation, FSH levels peak, signaling the ovary to release an egg. Once ovulation has occurred, levels return to or dip slightly below the baseline. Normal baseline levels are between 4.7 and 21.5 mIU/ml in women who are menstruating.

Certain medications, such as birth control pills, clomiphene, digitalis, and levodopa, can alter the test results.

Your doctor will instruct you to stop taking those drugs before taking an FSH test. In the case of hormonal birth control, it should be stopped at least 4 weeks prior to the test.

FSH and Pregnancy Planning

Since women with PCOS have low FSH levels and therefore do not ovulate regularly, she will typically see a fertility specialist or reproductive endocrinology for help in getting pregnant when the time is right.

Reproductive endocrinologists use a form of FSH to stimulate the ovaries to produce egg follicles for either IUI (intrauterine insemination) or IVF (in vitro fertilization). These are injectable medications, most commonly known as Gonal-f, Follistim and Bravelle.

Many women are often anxious to hear they will need to take shots to stimulate ovulation. While injections may be uncomfortable, it's important to keep your eyes on the bigger picture — having a baby.

For more information about how to give yourself an injection, read How Do I Give Myself Injections of Prescription Medicine?

FSH and Ovarian Reserve

In women who want to become pregnant later in life, FSH levels are used to test ovarian reserve — the amount of eggs a woman has left and the quality of those eggs. 

Your doctor will have blood work drawn on the third day of your menstrual cycle. The results are typically available within 24 hours depending on the lab.

Baseline FSH levels rise as women enter perimenopause, indicating a decreased amount of eggs left.

Perimenopause lasts 4 years on average and ends when a women has not had a period in 12 months. At that point, menopause begins. FSH levels at menopause are consistently elevated to 30 mIU/mL and above.

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